Juniper IGP - CONFIGURATION GUIDE V11.1.X Configuration Manual page 61

NOTE: For detailed information about the commands for configuring RTR probes,
see "Response Time Reporter" on page 65.
interface fastEthernet
NOTE: For more details on use of this command, see the syntax description in the
JUNOSe Command Reference Guide.
interface loopback
BEST PRACTICE: We recommend that you configure a 32-bit subnet mask for the
loopback interface. For example, if you configure a loopback interface with the IP
address and mask as 1.1.1.1/16, the 1.1.0.0/16 route entry is entered on the line
module and all traffic destined to the to 1.1.0.0/16 subnet is forwarded to the SRP
module by the line module. Although the SRP module responds only to traffic destined
to the 1.1.1.1 subnet and discards traffic to all other host IP addresses within that
subnet (1.1.1.1/16), if no specific or longer route entry is found or if the SRP module
receives too much traffic from subnets other than 1.1.1.1, the CPU utilization on the
SRP module reaches the saturation level.
If you use a subnet mask other than a /32 mask for the IP address configured on the
loopback interface, traffic from the entire subnet is routed to the loopback interface.
Therefore, that subnet cannot be routed through any other interface on the router,
unless a more specific route points to another interface.
Use to select a Fast Ethernet (FE) interface on a line module or an SRP module.
Example
host1(config)#interface fastEthernet 1/0
Use the no version to remove IP from an interface or subinterface. You must
issue the no version from the highest level down; you cannot remove an interface
or a subinterface if the one above it still exists.
See interface fastEthernet
Use to access and configure a loopback interface.
You can use a loopback interface to provide a stable IP address that can minimize
the impact if a physical interface goes down.
Example
host1(config)#interface loopback 10
host1(config-if)#ip address 100.20.32.1 255.255.255.255
You cannot shutdown a loopback interface.
Chapter 1: Configuring IP
37
IP Routing